1. Field of the Invention
The present invention relates generally to a method for manufacturing zinc oxide (“ZnO”) nanowires, and more particularly to a method for manufacturing zinc oxide nanowires using a ZnO seed layer containing a hydroxyl group and a device having the same.
2. Description of the Related Art
ZnO is a direct-transition-type oxide semiconductor material having a wide band gap energy of 3.37 eV in a hexagonal wurzite crystal structure, and has a large exciton bonding energy at room temperature. ZnO has high transmittance, a high index of refraction, and a large piezoelectric constant in the visible range of the electromagnetic spectrum. Because of these properties, ZnO is used in diverse ways including use in photonic crystals, optical modulator waveguides, varistors, transparent electrodes for use in solar cells, surface acoustic wave filters, light-emitting devices such as laser diodes, flat-panel displays, field emission displays (“FEDs”), photodetectors, gas sensors, UV shielding films, and including many other uses.
Although most previous uses of ZnO in electronic devices utilize a thin-film format, the use of ZnO nanorods and nanowires with a nano structure are becoming more widespread. ZnO nanowires yield their maximum efficiency by increasing the critical current density. A coating of ZnO nanowires can be used to increase the exposed area of, and therefore the photocatalytic efficiency of, a glass substrate.
Conventional methods for manufacturing ZnO nanowires include synthesis in solution, thermal chemical vapor deposition, metal organic chemical vapor deposition (“MOCVD”), molecular beam deposition, sol-gel deposition, sputtering processes, evaporation, spray pyrolysis, pulse laser deposition, and others.
The simplest process for manufacturing ZnO nanowires among those listed above is synthesis in solution, in which a substrate having a thin ZnO seed layer formed thereon is dipped in a mixed solution containing zinc nitrate Zn(NO3)2.H2O and hexamethylenetetramine (“HMTA”), and ZnO nanowires are grown therefrom at a temperature of about 95° C. (See Chem. Mater. 2005, VOL. 17, pp. 1001-1006)
Another common manufacturing technique is thermal chemical vapor deposition. For example, an alumina substrate is dipped in a solution containing catalytic metal particles, Ni(NO3)2 and ethanol, dried, and then put in a quartz boat filled with Zn powder inside a reactor. Later, the quartz boat is heated to about 450° C. while flowing about 500 sccm of Ar gas therein, and heat treatment is carried out at a temperature range of 450° C. to 950° C. for one hour to yield ZnO nanowires. (See Korean Patent Application Publication No. 2005-0005122).
However, the conventional techniques have limits to the precision of control they can exercise over the diameter of a ZnO nanowire during the manufacturing process. The conventional control technique of adjusting the surrounding atmosphere's conditions, e.g., vacuum condition, gas partial pressure, temperature and so on, has not been able to reduce the diameter of ZnO nanowires.